Heretofore, various herbicides have been developed and put into practical use for the purpose of protecting crop plants in agricultural fields and controlling weeds in non-agricultural fields. In general, the application form of such herbicides may be a solid preparation to be directly spread such as dust or granules, a solid preparation to be diluted with water and spread at the time of its use such as a wettable powder or water dispersible granules, or a liquid suspension comprising an active ingredient together with a surfactant, etc. suspended in water, a vegetable oil or the like, to be diluted with water and spread at the time of its use.
When the solid preparation to be directly spread or the solid preparation to be diluted with water at the time of its use is handled, the user may aspirate the solid flying in the air at the time of its use in some cases, and to avoid this, the liquid suspension is preferred. Further, in order to easily measure and adjust the amount of the preparation from such a reason that the area of the site to which the preparation is to be applied is different from the area per package of the preparation, a liquid preparation which can easily be measured by e.g. a scale on a preparation bottle is advantageous to a solid preparation which requires a meter such as a balance to measure its weight. Further, among liquid suspensions, a suspension in a vegetable oil is used for agricultural fields for grain in many cases, and when such a suspension in a vegetable oil is applied to non-agricultural fields such as roads, railway tracks, factory sites and play grounds, orchards and mulberry fields, the vegetable oil component will temporarily remain on the ground after the application, such being inconvenient when the field is used after the application. Further, it is preferred not to use an organic solvent, etc. to be used for an emulsifiable concentrate, etc. as far as possible in view of the influence over the environment at the application site and flammability of the preparation. Therefore, it has been desired to prepare a water-based herbicidal suspension having an active ingredient stably suspended in water.
As a compound to be incorporated as an active ingredient for herbicides, a sulfonylurea compound or its salt has been used as an active ingredient for various herbicides since it is a compound having excellent herbicidal effects with a relatively small amount of application. However, the sulfonylurea compound or its salt to be incorporated as a herbicidally active ingredient tends to easily decompose during preservation. If the active ingredient concentration in the preparation decreases by the decomposition, no expected herbicidal effect will be achieved at the time of application, or the internal pressure in a storage container for the suspension may increase during the preservation by generation of a gas due to the decomposition, which leads to blowing of the suspension at the time of opening and cause various inconvenience such as stains on the user or the circumference with the content.
Heretofore, addition of various compounds has been studied so as to prevent decomposition of the sulfonylurea compound or its salt to be incorporated as a herbicidally active ingredient. For example, JP-A-2000-159603 discloses a water-based herbicidal suspension comprising a herbicidal sulfonylurea compound and a phenol sulfonate or its formaldehyde condensate.
Further, JP-A-59-205305 discloses a water-based herbicidal suspension comprising a salt'of a herbicidal sulfonylurea compound and an ammonium or alkali metal salt of a carboxylic acid or an inorganic acid. Specifically, it is disclosed that at the time of preparation of the water-based herbicidal suspension, a herbicidal sulfonylurea compound and a surfactant are mixed in water, and an ammonium salt or an alkali metal salt of a carboxylic acid or an inorganic acid is charged thereto, whereby a salt of the herbicidal sulfonylurea compound is formed and precipitated, and the precipitated salt of the herbicidal sulfonylurea compound is dispersed in water by e.g. a wet-mill.
Further, Japanese Patent No. 3,175,850 discloses preparation of a water-based suspension of pyrazosulfuron by employing an inorganic acid, an organic acid or a buffer solution.